Last modified by Microchip on 2023/11/09 08:59

Op amps are normally not used in an open-loop configuration except when being used as comparators and/or oscillators due to their extremely high open-loop gain. When used as a comparator, an op amp compares two voltages or currents and switches its outputs to indicate which is larger.

A standard op-amp used as a comparator is shown in the accompanying figure.

comparator model

Vout = VDD when V1 > V2
Vout = VSS when V1 < V2

When the non-inverting voltage input (V+) is higher than the inverting input (V-), the high gain of the op amp causes it to output the most positive voltage it can possibly be (positive rail). When the non-inverting input (V+ ) drops below the inverting input (V- ), the op amp outputs the most negative voltage it can possibly be (negative rail).